Device for mixing small quantities of liquids

ABSTRACT

A device for mixing very small quantities of liquids comprises at least one mixing element with at least one inlet channel and at least one outlet channel; at least two microchannels issue from the inlet channel, all such issuing channels lying in a single branching plane. The microchannels are led to a confluence element in a plane which is rotated 90 degrees in relation to the branching plane. The mixer element is arranged in the planar surface of a substrate, the planar surface being hermetically sealed by a covering. The invention concerns a device for mixing liquids in which mixing is effected by the flow of the liquids to be mixed through narrow channels.

The-invention relates to a device for mixing liquids, in which themixing takes place while the liquids to be mixed are flowing throughnarrow channels.

Devices for mixing liquids are known in the prior art in the form ofstatic or dynamic mixers. Static mixers generally consist of pipesystems with internal fixtures. By utilizing the kinetic energy of aflowing liquid, it is homogenized after a specific flow path. Dynamicmixers have rotating mixing tools. These cause the mixing energy toenter the mixing product and bring about homogenization. Owing to thesize of the equipment, mixers of this type can only be used for largequantities of liquid. However, the end or intermediate productsoccurring are often not required in this quantity.

By an extreme reduction in the reaction environment, attempts have beenmade to provide arrangements which enable mixing with little use ofmaterial. Such mixers operate as static mixers for the homogeneousmixing of small quantities of liquid according to the principle of thediffusion of liquid particles. In Proceedings μ-TAS; Enschede 1994;pages 142-151; ISBN 0-7923-3217-2, a device is described, in which theliquids flow through narrow channels and become mixed by diffusion aftercorrespondingly long flow paths. In these arrangements, the highpressure loss and low degree of efficiency have proved to be adisadvantage.

A further design of static mixers is described in Proceedings μ-TAS;Enschede 1994; page 79. This arrangement has a large number of nozzlesthrough which the liquids to be mixed are forced into one another. Inthese designs, too, the high pressure loss and the low degree ofefficiency are a disadvantage.

Furthermore, mixers are known, which have a complicated shape of thechannels, and in which, by means of internal fixtures, rotation and thusmixing of the liquid is to be brought about, a division of the liquiddisadvantageously taking place after each mixing element and, after thefollowing element, the division again leading to mechanical separationof the liquid (Proceedings μ-TAS; Enschede 1994; pages 237-243). Theknown mixers for small quantities of liquid are either of verycomplicated construction or they have a very low degree of efficiency.

The invention is based on the object of specifying a device which canhomogenize even very small quantities of liquids with high efficiencyand is simple to manufacture.

According to the invention, the object is achieved in that

the device consists of at least one mixing element which has at leastone inlet channel and at least one outlet channel,

at least two microchannels issue from the inlet channel, all the issuingchannels lying in one branching plane,

the microchannels are led to a confluence element, the inflow beingeffected in one plane which is arranged rotated through 90° relative tothe branching plane and

the mixing element is arranged in the planar surface of a substrate, theplanar surface of the substrate being hermetically tightly sealed by acovering.

Advantageous refinements of the arrangement according to the inventionare specified in the subclaims.

The device according to the invention is suitable for mixing very smallquantities of liquid with a high efficiency and is distinguished by avery small construction size. Each element has at least two inletchannels for the liquids to be mixed. These channels can be arranged ina vertical or a horizontal plane. In the flow direction, these channelsmeet at a point, the confluence element. This is designed in such a waythat, with a horizontal position of n inlet channels, n-outlet channelsissue from this confluence in n different vertical planes respectively.If the n inlet channels lie in a vertical plane, n outlet channels issuefrom said confluence in a horizontal plane. The outlet channels, inturn, then form the inlet channels for the following mixing element. Theoverall arrangement consists of a large number, but of at least two,interconnections of these elements. Mixing of the liquids is achieved inthat, for example, two liquids flowing in horizontal flow channels meetone another at the confluence in such a way that a vertical boundarylayer develops between the two liquids. Two outlet channels then issuefrom this confluence in two planes disposed perpendicular to oneanother. This brings about a vertical separation of the overall flow. Afirst part-flow flows in a first plane. The second part-flow flows in asecond plane. Before the next confluence is reached, the two part-flowsare guided in one plane again. At the confluence, a liquid flow thusdevelops, which has four liquid layers with three boundary layers.Outlet channels also issue from this confluence, again arrangedperpendicularly. Again these open in one plane in the next confluence.At this confluence, the number of boundary layers in the liquid isseven.

The outlet channels are designed in each case in such a way that theflow path of the liquids is equally long or the flow resistance is ofequal magnitude. The elements are manufactured using microstructurablematerials. They can be arranged one after another or one above another.The following elements can be arranged rotated through any desiredangle, preferably through 90°, relative to the preceding element.

The invention is explained in greater detail below with reference to anexemplary embodiment. In the associated drawing,

FIG. 1a shows the basic arrangement of a mixing element for-verticalseparation and horizontal layering of the liquids one above another,

FIG. 1b shows a basic arrangement of a mixing element for horizontalseparation and adjacent vertical layering of the liquids,

FIG. 2 shows the front view of a mixing element with an inlet substrateplate, a structured substrate plate and a covering plate,

FIG. 3 shows the front view of a mixing element consisting of twostructured substrates,

FIG. 4 shows the front view of a mixing element consisting of twostructured substrates and the lateral arrangement of the inlets andoutlets of the mixing element,

FIG. 5 shows the front view of a mixing element consisting of twostructured substrates and the arrangement of the inlets and outlets ofthe mixing element in the upper substrate plate,

FIG. 6 shows the front view of a mixing element consisting of threestructured substrate plates,

FIG. 7 shows the front view of a mixing element consisting of all thestructures in a substrate,

FIG. 8 shows the front view of a mixing element for mixing more than twofluids consisting of two structured substrate plates and laterallyarranged liquid inlets and outlets,

FIG. 9 shows the front view of a mixing element for mixing more than twofluids consisting of two structured substrate plates and liquid inletsand outlets which are arranged in the upper substrate,

FIG. 10 shows the plan view of a possible connection of a plurality ofmixing elements of an arrangement one behind the other with threesubstrates, and

FIG. 11 shows the sectional illustration of the arrangement 10.

FIG. 1a diagrammatically illustrates the basic arrangement of a mixingelement. In the case of this mixing element, the liquid to behomogenized is conducted into the mixing element through a microchannelat the inlet 1. This microchannel has a bifurcation 2 from which themicrochannels 3 and 4 issue. The bifurcation 2 brings about a separationof the liquid along an imaginary vertical line. The mixing elements maybe arranged one after another several times over. For mixing elementswhich are arranged at the beginning, the inflow of the liquids to bemixed takes place through the cross-sectional areas 1.1 and 1.2. Theinlet 1, the cross-sectional areas 1.1 and 1.2, the bifurcation 2 andthe microchannels 3,4 are located in a horizontal plane. The followingmicrochannels are arranged in such a way that microchannel 6 departsfrom this plane. The microchannel 5 remains in the horizontal plane. Themicrochannels 5 and 6 are arranged in such a way that they meet again ina confluence element 7, the two microchannels 5 and 6 being located indifferent planes. The liquids flowing out of the microchannels 5 and 6thus undergo layering one above another at the confluence element 7along an imaginary horizontal line. After the liquids have passedthrough the confluence element 7, they flow into a further microchannel8. This microchannel 8 forms in its shape a new inlet for a followingmixing element or, in the case of being the last mixing element, leadsto the outlet of the micromixer.

FIG. 1b illustrates the diagrammatic basic arrangement of a mixingelement, in which the liquid to be homogenized is conducted into themixing element through a microchannel at inlet 1. This microchannelopens into the bifurcation 2 from which the microchannels 3 and 4 issue.In the bifurcation 2, the liquid is separated along an imaginaryhorizontal line. For mixing elements which are arranged at thebeginning, the inflow of the different liquids takes place through thecross-sectional areas 1.1 and 1.2. In the case of this mixing element,the inlet 1, the cross-sectional areas 1.1 and 1.2 and the microchannels3 and 4 are located in two horizontal planes. The bifurcation- 2connects the two horizontal planes through a shaped opening. In thefurther course of the microchannels, one of the microchannels 4 departsfrom the horizontal plane while the microchannel 3 remains there. Themixing channels 5 and 6 are arranged in such a way that they meet againin the confluence element 7. Since, however, both microchannels 5 and 6lie in the same horizontal plane, the liquids flowing out of themicrochannels 5 and 6 undergo adjacent layering at the confluenceelement 7 along an imaginary vertical line. A further microchannel 8 isarranged downstream of the confluence element 7. This microchannel formsin its shape a new inlet for a following mixing element or, in the caseof being the last mixing element, leads to the outlet of the micromixer.

FIG. 2 illustrates a mixing element which is located in a planarsubstrate 10. A further substrate 11 is arranged on the top side of thesubstrate 10. The substrate 11 contains the inlets 12 and 13 into themixing element and the outlet 14 out of the mixer. Any desired number ofmixing elements may be arranged in the substrate 10. The position of theinlets 12 and 13 and of the outlet 14 in relation to the position of themixing elements are sic! illustrated by arrows 15a, 15b and 15c. In thiscase, in the first mixing element of a micromixer, the inlets 12 and 13are positioned on the substrate 11 in such a way that they are directlyconnected to the microchannels 16 and 17 of the substrate 10. Thesubstrates 10 and 11 are connected to one another in a hermeticallysealed manner. The microchannels 16 and 17 are arranged adjacently inthe substrate 10. The liquids fed through the microchannels 16 and 17are conducted one above the other in the microchannel 18. The liquidflows coming out of the two microchannels 16 and 18 meet again at theconnection 19, the liquid flow from microchannel 16 lying in a differenthorizontal plane at this junction than the liquid flow from microchannel18. Starting from the connection 19, the liquid flow from microchannel18a continues in the second plane of the substrate 10 up to thebifurcation 20. Two microchannels 21 and 22 again issue from thebifurcation 20, so that the liquid flow starting from the microchannel22 remains in the second horizontal plane of the substrate 10, whereasthe second liquid flow starting from microchannel 21 departs from thishorizontal plane and opens sic! into a microchannel 23 in the firsthorizontal plane of the substrate 10. The two liquid flows from themicrochannels 22 and 23 which are located in different horizontal planesof the substrate 10 meet again at the connection 24, the liquid flowcoming from channel 22 lying in a different horizontal plane at thisconnection 24 than that from channel 23. Issuing from the connection 24,the microchannel 23a continues in the first plane of the substrate 10 upto the bifurcation 25. At this bifurcation 25, two liquid flows from themicrochannels 16a, 17a are again formed. The microchannels 16a and 17aare the inlet channels for a further mixing element. In the case ofbeing the last mixing element, an opening is arranged in the substrate11 in such a way that it is directly connected to the channel 23a in thesubstrate 10. The entire substrate 10 on which the structures of all themixing elements are located is hermetically tightly sealed on theunderside by a further substrate 26.

A further embodiment of the mixing element is shown in FIG. 3. Themixing element is implemented by two substrates 30 and 31 which arehermetically tightly connected to one another. Microchannels 32, 33 and34 are formed in the top side of the substrate 31 which is a horizontalplane. Each of these channels is isolated from the other channels 32, 33and 34 in the substrate 31. A microchannel structure which has differentsections is likewise formed in the underside of the substrate 30 whichis a further horizontal plane. In the first section 35, the microchannelis shaped to be straight. A bifurcation 36 adjoins this section. Issuingfrom this bifurcation 36, two new microchannels 37 and 38 are formed. Inthis case, the microchannels of the substrate 30 are assigned to thesecond substrate 31 in such a way that the ends of the microchannels 32,33 come into direct contact with the channel 35. Furthermore, the endsof the microchannels 37, 38 are arranged in such a way that coveringwith the microchannel 34 of the second substrate 31 is possible.

Located in the underside of the substrate 30 is a microchannel 39 whichcovers the ends of the channels 32 and 33 in the substrate 31. Thismicrochannel 39 has an entry surface 40 for the liquids to be mixed. Theoutlet of the mixing element is formed by the microchannel 41 with theexit surface 42.

An expedient arrangement of the liquid entries and liquid exits is shownin FIG. 4. Located in the first substrate 30 are the microchannels 47and 48 which cover the microchannels 53 and 54 in the second substrate31 over their entire width and whose ends likewise cover themicrochannels 32 and 33 of the substrate 31. Together with themicrochannels 47 and 48 of the first substrate 30, the microchannels 53and 54 of the second substrate 30 form entry surfaces 45 and 46 for theliquids to be mixed. The liquid exit is formed by the covering of themicrochannel 49 in the first substrate 30 and the microchannel 55 in thesecond substrate 31. By means of this covering of the two microchannels49 and 55, a common exit surface is obtained. There is no illustrationof the fact that, for fluid contacting, capillary tubes which are sealedoff at their circumference from the substrates 30 and 31 can also bepushed through the entry surfaces 45 and 46 and the exit surfaces 50.

A further possibility of exterior fluid contacting of the micromixingelements is illustrated in FIG. 5. The substrate 30 has shaped openings56 which cover the ends of the microchannels 32 and 33 in the substrate31. These openings are designed in such a way that inflow of the liquidsto be mixed into the mixing element is possible. The outlet of themixing element is likewise formed by an opening 57 in the substrate 30.In this case, said opening 57 is arranged in such a way that it coversthe end of the microchannel 34 in the substrate 31. There is noillustration of the fact that tubes are arranged on the surface of thesubstrate 30, the entry cross section of said tubes being arrangedparallel to the surface of the substrate.

In a further exemplary embodiment according to FIG. 6, a mixing elementis shown, which is made up of a total of three substrates. The inflowchannels 63 and 64 are located in a first substrate 60. The ends of saidinflow channels are arranged in the flow direction to two microchannelsections 67 and 69 in the second substrate 61 in such a way thatcovering occurs. The microchannel sections 67 and 69 open into aconfluence element 68. The confluence element 68 is covered on its topside by the microchannel 65 of the substrate 60 and on its underside bythe microchannel 66 of the third substrate 62. The microchannels 65 and66 are shaped in such a way that, viewed in the flow direction, they arecongruent with the microchannel sections 70 and 71 in the secondsubstrate 61. The microchannel sections 70 and 71 open into a confluenceelement 72. Issuing from this point is a new microchannel 73 whichconnects the mixing element to further mixing elements.

FIG. 7 shows a mixing element in which all the structures are located ona substrate 75. The inlet channel 77 for a liquid is arranged in theupper plane of the substrate 75. Located in the lower plane of the samesubstrate 75 is the inlet channel 76 for a second liquid. Bothmicrochannels open into a confluence element 78 which is designed insuch a way that two new microchannels 79 and 80 issue in the lower planeof the substrate. In this case, the confluence element 78 is designed insuch a way that it connects the upper and the lower plane of thesubstrate 75 to one another. One of the microchannels 80 remains in itsfurther course in the lower plane of the substrate 75. The secondmicrochannel 79 opens into an opening 81 between the upper and the lowerplane of the substrate 75. Issuing from this opening 81 is a newmicrochannel 82 in the upper plane of the substrate 75, which finallyagain opens into a confluence element 83 which is of similar design tothe confluence element 78. Again two microchannels 80 and 81 issue fromthis confluence element 83 in the upper plane of the substrate. In thiscase, the dashed line defines the end of a mixing element and thetransition to a new mixing element. The inlets 76 and 77 can be used tooperate the mixing elements. In this case, the outlets are formed by thechannels 80 and 81. It is likewise possible to design the channels 80and 81 as inlets of the mixing element. In this case, the outlet of themixing element is formed by the channels 76 and 77.

FIG. 8 shows a mixing element that is suitable for mixing more than twodifferent liquids. The microchannels 85, 86, 87 and 88 are designed forthe liquid entry. These channels are connected to one another in such away that layering of the individual liquids one above another isinevitably brought about in the microchannel 89. At the branching point90, the microchannel is divided into the same number of microchannels 92as are formed at the liquid entry. The microchannels 92 are connected toone another at their ends by the microchannel 91. The exit is formed bythe microchannel 93.

FIG. 9 shows a further possibility for mixing more than two differentliquids. The liquid entries 93 are connected to the microchannels 94, 95and 96 in the second plane of the mixing element. The microchannels 94,95 and 96 open at their ends into the channel 97 in the first plane ofthe mixing element. Located at its one end is a branching point 98 fromwhich at least two, here the microchannels 99 and 100 lacuna! in thesecond plane of the mixing element. An exit 102 from the mixing elementis arranged at one end of the microchannel 101.

FIG. 10 shows the plan view of an interconnection of a plurality ofmixing elements. For reasons of clarity, the upper substrate was notillustrated. The solid lines 103 show the structure of the microchannelsin the first plane. The structure of the second plane is represented bydashed lines 104. Openings between the planes are located at thecovering points 105 of the structures of the two planes. FIG. 11 shows asectional illustration of FIG. 10, the covering substrate 106 with theentry openings 107 and an exit opening 108 being illustrated. Thechannel structures 109 and the openings 110 in the substrate 11 areclearly visible. The underside of the structured substrate 111 iscovered by a further substrate 112.

We claim:
 1. A device for mixing liquids, wherein mixing is effected bythe flowing of the liquids through narrow channels, said devicecomprising:at least one mixing element having at least one inlet channeland at least one outlet channel, wherein said mixing element is arrangedon at least one substrate having planar surface; at least twomicrochannels issuing from said inlet channel, said at least twomicrochannels lying in a same branching plane; a confluence elementbeing connected by a connection to said microchannels, wherein theconnection effects a 90° rotation of the inflow of the liquid relativeto said branching plane as the liquid flows from said microchannels tosaid confluence element; said at least one outlet channel beingconnected to said confluence element; and a covering hermeticallysealing the planar surface of said at least one substrate to cover themixing element.
 2. The device according to claim 1, wherein said atleast one outlet channel is in a plane parallel to a plane of the inletchannels; and, said device further comprising one or more openingthrough which said at least one outlet channel is fed back into saidplane of said at least one inlet channel.
 3. The device according toclaim 2, wherein said microchannels and said openings are produced bychemical etching processes, laser etching, photo-etching, or sandblasting.
 4. The device according to claim 2, wherein said confluenceelement comprises one or more openings issuing to a connecting channelon a following plane; and, wherein additional channels issue from saidconnecting channel for mixing.
 5. The device according to claim 1,wherein said confluence element comprises one or more opening issuing toa connecting channel on a following plane; and, wherein additionalchannels issue from said connection channel for mixing.
 6. The deviceaccording to claim 1, wherein all of said outlet channels issuing fromsaid confluence element have substantially the same flow resistance. 7.The device according to claim 6, wherein two or more of said mixingelements are arranged successively in one plane, and wherein each mixingelement is rotated relative to a preceding mixing element.
 8. The deviceaccording to claim 1, wherein two or more of said mixing elements arearranged successively in one plane, and each mixing element is rotatedrelative to a preceding mixing element.
 9. The device according to claim8, wherein each mixing element is rotated 90° relative to a precedingmixing element.
 10. The device according to claim 8, further comprisingan intermediate layer between raid substrates and openings forconnection between said substrates.
 11. The device according to claim 1,wherein said covering consists of silicon or glass.
 12. The deviceaccording to claim 1, wherein said microchannels are located on aseparate substrate from said confluence element.
 13. The deviceaccording to claim 1, further comprising an intermediate layer betweensaid substrates and openings for communication between said substrates.14. The device according to claim 1, wherein said one or more substrateis comprised of single-crystalline silicon or etchable glass etched bymicroscopic techniques.
 15. A device for mixing liquids having multiplesubstrates with planar surfaces, comprising:one or more mixing element,each mixing element comprising at least one inlet channel and at leaseone outlet channel; two or more microchannels issued from said inletchannel, said microchannels being coplanar on a first substrate andconducting liquid flow in a first plane parallel to said firstsubstrate; a confluence element lying on a second substrate; openings onsaid first substrate and said second substrate; said confluence elementbeing connected to said microchannels via said openings; wherein saidopenings provide a perpendicular rotation of the inflow of the liquidsrelative to said first plane as the liquid flows from said firstsubstrate to said second substrate; and said outlet channel beingconnected to said confluence element; whereby the inflow of the liquidsthrough said inlet channel, said microchannels, said openings, saidconfluence element, and said outlet channel results in homogenizedliquids at said outlet of said outlet channel.
 16. The device as claimedin claim 15, said device comprising an interconnection of a plurality ofsaid mixing elements, wherein said outlet of one element becomes saidinlet of a following mixing element.
 17. The device as claimed in claim16, further comprising a covering to hermetically seal a planar surfaceof one of said substrate.
 18. The device as claimed in claim 16, furthercomprising an intermediate layer between said substrates, saidintermediate layer comprising openings for conducting the liquids fromone substrate to another.
 19. The device as claimed in claim 16, whereinall of said outlet channels have substantially same flow resistance. 20.The device as claimed in claim 15, wherein all of said outlet channelshave substantially same flow resistance.